“Luna, what’s in here?” Teigen can be heard saying in the background of the clip, with baby Luna pointing at her mom’s stomach and saying, “Baby!”

Legend — who commented jokingly on his wife’s Tuesday post with, “Maury will have the final word on this” — spoke to PEOPLE Friday, revealing the couple were “working on” baby No. 2 and that “hopefully it will be soon.”

As far as Luna’s big-sister capabilities? “I have no idea,” said the singer, adding, “She is very sweet and she likes to share, so hopefully that will translate.”

The model mama-to-be opened up to E! Newsearlier this month about adding to her family, staying mum on her pregnancy but hinting that a new baby might be coming sooner rather than later.

“We’re still trying … I’m going for, I mean hopefully in the next few years, because for me I really want to just knock ’em out,” Teigen said, adding that she’s feeling “good.”

“That’s my dream, I want to just be pregnant kind of for the rest of my life,” she confessed. “Not for the rest of my life, but the rest of my fertile life. So we’ll see.”

“The first little girl didn’t work, and then the second is Luna,” she told InStyle for their November cover story, explaining that she and Legend started with 20 embryos, but that number was narrowed down to three after screening and based on what was “going to be good for [my] body.”

The sex of the couple’s second child on the way is unconfirmed at this point, but a son wouldn’t be a surprise. In January, they spoke with Entertainment Tonight at the 28th Annual Producers Guild Awards, where Teigen said with a smile, “A little boy is next, for sure.”

The Lip Sync Battlehost, 31, later clarified her comments on Twitter, writing, “Since this is coming up again, I said our next baby would be a boy because that is the embryo we have left. A boy. So. Yeah.”

The proud parents, whose baby girl has joined them on the road for Legend’s Darkness and Light Tour, have been open in the past about both the ups and downs of how having Luna has changed their lives.

“Diapers on the bus, a crib on the bus — a long way from my bachelor days,” the soon-to-be father of two, 38, told PEOPLE in April with a laugh, adding that the spouses’ time prioritization has shifted completely since they became a family of three.

“There are some things that I would’ve said yes to before that I say no to now,” the Tony, Grammy and Oscar winner explained. “And there are some choices that I’ll make now that I wouldn’t have made before.”

“I have really good days and really bad days, and I don’t tend to talk about the really bad days. But I would hate for people to think those days didn’t exist,” Teigen said in her InStyle November cover-story interview, noting of her initial reaction to her experience, “I thought I was just being a selfish a–hole.”